1. Field of the Invention
This invention relates generally to testing methods and apparatus for semiconductor devices. More particularly, the invention pertains to a method and apparatus for measuring localized temperatures present on semiconductor devices and the like for research and development purposes.
2. State of the Art
Modern integrated circuit (IC) devices are commonly formed by joining the electrically active bond pads of a semiconductor die to the conductive lead fingers of a leadframe with metal wires. The wire bonding process may comprise:
a. thermocompression bonding, which uses pressure and elevated temperature, typically 300-400.degree. C. to bond the wire ends to the bond pads and leadframe; PA1 b. thermosonic bonding, in which ultrasonic energy is combined with compression at temperatures of about 150.degree. C.; or PA1 c. ultrasonic bonding, in which ultrasonic energy is typically applied at ambient temperatures. This method is generally limited to some specific metals such as aluminum or aluminum alloy wires on aluminum or gold pads.
As is well known, the functionality of manufactured electronic devices depends upon successful bonding of the wires to the bond pads of the die and to the lead fingers.
In each of thermocompression bonding and thermosonic bonding, reliability of the bonding process depends upon the temperatures of the elements being joined.
It is important for a semiconductor device manufacturer to have the capability for evaluating the quality of conductor bonds, such as wirebonds, leadframe to bump bonds, etc. Evaluation of the bonding process includes, e.g., destructive ball shear tests and wire bond pull tests as well as contaminant tests such as by spectrographic analysis.
In addition, thermal analysis of the die and leadframe may be done during the conductor bonding operations to yield an indication as to wire bonding quality. Thus, for example, U.S. Pat. No. 5,500,502 of Horita et al. describes a process for bonding a leadframe to a bump using laser irradiation. The state of contact between the leadframe and the bump is then tested using the intensity of the emitted infrared radiation as a measure of the leadframe temperature. Knowing the time lapse between the laser radiation and the measured temperature, the temperature as a function of time may be calculated, particularly a threshold temperature correlated to bond effectiveness and the resulting quality of the wire bond.
The Horita et al. method does not address the testing of wirebonds. Furthermore, the method depends upon the emission and reflection of infrared radiation, which varies with the surface characteristics of the material whose temperature is being measured. As is well known, both semiconductor dies and leadframes are made of a variety of materials, each of which may have a differing emission/reflection temperature function when laser-irradiated. In addition, a wide variety of materials is used for doping semiconductor dice and for coating dice. For example, U.S. Pat. No. 5,256,566 of Bailey teaches the coating of dice with polysilicon. Thus, the infrared temperature meter must be calibrated for each material, making temperature measurements labor intensive.
Furthermore, the presence of contaminants on the die or leadframe surfaces will affect the accuracy of the Horita et al. method.
A method and apparatus for accurately measuring the temperature of very small areas of surfaces, independent of the surface composition, are desirable for research and development purposes in the semiconductor die area.